Abstract of the Disclosure

A method for forming a narrow, such as a submicrometer, dimensioned mask opening on a silicon body involving forming a first insulator region having substantially a horizontal surface and a substantially vertical surface. A second insulator is applied on both the horizontal surface and substantially vertical surfaces. The second insulator is composed of a material different from that of the first insulator layer. Reactive ion etching of the second layer removes the horizontal layer and provides a narrow dimensioned second insulator region on the silicon body. The surface of the silicon body is then thermally oxidized. The narrow dimensioned second insulator region is removed to form a narrow dimensioned mask opening